Determination of serum carcinoembryonic antigen (CEA) levels in healthy non-smokers and smokers shows a progressive increase with age in each group and a consistently higher level in smokers. The results show that the currently used upper limit of normal for this assay is applicable only to nonsmokers of approximately 40 years of age. These findings may increase the utility of the assay as a marker for tumor presence in malignancies associated with elevations of CEA levels. CEA levels in head and neck cancer are elevated only in the presence of clinically manifest disease, thus diminishing the value of this assay as a tumor marker in such patients. Serum carbohydrates and serum glycoproteins show correlations with tumor burden in a variety of solid malignancies. In addition, certain carbohydrates and glycoproteins show an inverse relationship with in vitro lymphocyte reactivity. The studies indicate that additional investigations are warranted to determine the value of these moieties as a marker of tumor burden and correlate of immune reactivity in cancer patients. n patien